In yeast, transfer RNA genes are transcribed by RNA polymerase III and most structural genes by RNA polymerase II. The specific structural features of the beginnings and ends of yeast genes which lead to RNA polymerase recognition are being explored in this project. For the tRNA Tyr SUP4 gene, promotor mutants have been obtained by selecting against strains which possess functional ochre suppressors. The sequence changes for a collection of such mutants have been determined by molecular cloning and DNA sequencing. Subsequent characterization of these and other SUP4 loss-of-suppression mutants includes a test of their ability to be the RNA processing of these in vitro transcripts.